The estimate of emission region locations of {\it Fermi} FSRQs

TL;DR

This study models the spectral energy distributions of 21 Fermi FSRQs to estimate the locations of their emission regions, considering BLR structure and absorption effects, revealing correlations with accretion disk luminosity.

Contribution

It introduces a detailed multi-component one-zone leptonic model that accounts for BLR structure and absorption to constrain emission region locations in FSRQs.

Findings

Emission regions are within 7.9×10^{16} to 1.3×10^{18} cm for low luminosity FSRQs.

High luminosity FSRQs have emission regions between 2.6×10^{17} and 4.2×10^{18} cm.

External Compton-BLR component significantly contributes to gamma-ray emission.

Abstract

We study the locations of emission regions through modelling the quasi-simultaneous multi-frequency spectral energy distributions of 21 {\it Fermi} flat spectrum radio quasars (FSRQs) in the frame of a multi-component one-zone leptonic model. In our calculations, we take the detailed broad line region (BLR) structure into account and discuss the effect of the uncertainty of the BLR structure on constraining the location of the emission regions for each FSQR, meanwhile we also include both the internal and external absorptions. Our results indicate that (1) the contribution of external Compton-BLR component is important to $\gamma$-ray emission, and the energy density of external target photon fields depends on the location of the emission region, which can be derived through reproducing the observed $\gamma$-ray emission, and (2) the emission regions of FSRQs with relative low accretion disk luminosity lie in the region of $7.9\times10^{16}$\ --\ $1.3\times10^{18}$\ cm (300 -- 4300 Schwarzschild radii) from central black hole, and for FSRQs with high accretion disk luminosity, the emission regions locate in the larger region of $2.6\times10^{17}$\ --\ $4.2\times10^{18}$\ cm (300 -- 5600 Schwarzschild radii).